Process for the production of triglycerides

ABSTRACT

A process for the production of triglycerides of C 1  -C 4  alkyl esters of C 6  -C 22  fatty acids: 
     a) where dry sodium carbonate catalyst is dissolved in glycerol and mixed with a molar excess of preferably the methyl ester of C 6  -C 22  fatty acid at a temperature between about 150° C. and 250° C. at less than atmospheric pressure and under substantially anhydrous conditions to produce an initial reaction mixture containing the corresponding triglycerides of said fatty acids, and partially reacted glycerol with unreacted hydroxyl groups (OH values 10-40), 
     b) thereafter, a portion of the initial reaction mixture is reacted with additional C 1  -C 4  alkyl ester of C 6  -C 22  fatty acid under conditions to achieve substantially full conversion of said unreacted hydroxyl groups (OH values of 5 or less), and 
     c) a product containing the corresponding triglycerides of said fatty acids is separated from unreacted alkyl ester and from the sodium carbonate catalyst. Improved light colored triglyceride products are achieved and can be separated readily from the sodium carbonate catalyst by filtration.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the production of triglyceridesof C₆ -C₂₂ fatty acids.

2. Statement of Related Art

In the production of methyl esters by reaction of oils, particularlycoconut oil or palm kernel oil, large quantities of so-called first-cutmethyl esters, i.e. C₈ -C₁₂ methyl esters, are inevitably formed due tothe nature of the starting material. The quantity in which thesefirst-cut methyl esters are formed is generally greater than the demand,so that there is considerable interest in a process for the productionof triglycerides from the corresponding short-chain methyl estermixtures directly, i.e. without preliminary conversion of the methylesters into the corresponding fatty acids.

Processes for the production of triglycerides of the type mentionedabove are known in which sodium methylate and sodium hydroxide are usedas alkaline catalysts. However, the triglycerides obtained are dark incolor and require elaborate purification for use in the food industry.In addition, the reaction systems show a tendency towardsemulsification, in addition to which the sodium salts of the fatty acidsformed as secondary products are difficult to remove.

DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein are to be understood as modified in all instances by the term"about".

The present invention is directed to a process for the production oftriglycerides of C₆ -C₂₂ fatty acids, and more particularlytriglycerides of C₆ -C₁₂ fatty acids by the reaction of C₁ -C₄ alkylesters of the fatty acids with glycerol in the presence of an alkalimetal carbonate catalyst and glycerol.

The triglycerides produced in accordance with this invention includelight colored products which are especially useful. These products havea wide range of commercial applications. Triglycerides derived fromshort-chain (C₆ -C₁₂) fatty acids are marketed, for example, under thename Delios®. The products are used as components of aromas andessences, for the surface treatment of dried fruits and tacky candygoods, and as base oils for the production of release agents for theconfectionary field, and the like.

More specifically, one embodiment of the process according to thisinvention comprises the following steps and conditions:

a) A mixture of dry alkali metal carbonate, preferably sodium, potassiumor lithium carbonates, and glycerol is added to dried fatty acid alkylesters as described above which are heated to a temperature of 150° C.to 250° C. in a quantity corresponding to a molar ratio of glycerol tothe fatty acid alkyl ester of preferably between 0.15:1 to 0.30:1 and atsuch a rate that the glycerol preferably remains soluble in the reactionmixture. A slight excedence of solubility, e.g., up to 10% is alsoacceptable. The term substantially soluble is employed herein tocharacterize these conditions.

b) After addition of the glycerol, more fatty acid alkyl ester is addedto the boiling reaction mixture in a quantity preferably of at least10%, based on the fatty acid alkyl ester used in step a), to react anyunreacted hydroxyl groups of the glycerol.

c) The entire reaction is carried out under a light vacuum, i.e., lessthan atmospheric pressure, and C₁ -C₄ alcohols formed are continuouslydistilled off.

d) The fatty acid alkyl ester is removed by distillation from thereaction mixture obtained which consists predominantly of fatty acidtriglyceride, fatty acid alkyl ester and sodium carbonate.

e) Sodium carbonate is separated off and,

f) Fatty acid triglyceride is purified by conventional methods.

The molecular weight of the C₉ fatty acid alkyl ester is preferably usedas the basis for calculating the molecular weight of the fatty acidalkyl esters present in the form of a mixture. The addition of the fattyacid alkyl ester in step b) is also made to reduce the boiling point ofthe glyceride/fatty acid alkyl ester mixture.

It is essential to use substantially anhydrous reactants and catalystswhich include carefully dried fatty acid alkyl esters, glycerol andsodium carbonate. Water contents of 1% by weight in the reaction mixturecause the undesireable formation of soaps or emulsions. Water contentsof less than 1% and preferably less than 0.5% and most preferably lessthan 0.1% are employed in this invention.

The methyl ester is preferably used as the fatty acid alkyl ester.

In one advantageous embodiment of the invention, since the C₁ -C₄alcohol which is distilled off always contains appreciable fatty acidalkyl ester, this mixture is rectified and the fatty acid alkyl esterthus obtained is returned to the reaction mixture.

In another advantageous embodiment, it is also possible to introduce themixture of dry sodium carbonate in glycerol directly into therectification column during the reaction. A reaction to producetriglycerides takes place in the rectification column itself. Thetriglycerides thus formed are returned to the actual reaction mixturetogether with unreacted fatty acid alkyl ester.

In another advantageous embodiment of the invention, the process iscarried out continuously. This embodiment of the process comprises thefollowing steps and conditions:

a) A multi-plate, heatable reaction zone in communication and preferablysurmounted by a rectification zone is employed for the reaction process.The term multi-plate is understood to include conventional columnpacking materials as well as physical distillation trays as are wellknown in the art.

b) The glycerol/sodium carbonate solution is introduced into the upperpart of the reaction column preferably after heating it to the reactiontemperature.

c) The fatty acid alkyl ester is introduced into the middle part of thereaction column. The ester is optionally introduced in the form ofsuperheated vapor.

d) More fatty acid alkyl ester, also optionally as superheated vapor, isintroduced below the point at which the fatty acid alkyl ester is fedinto the reaction column in order to react any unreacted glycerol.

e) C₁ -C₄ alcohol and fatty acid alkyl ester are separated in therectification column and the C₁ -C₄ alcohol is distilled off overhead.

f) Triglyceride/fatty acid alkyl ester/sodium carbonate mixture isremoved from the sump of the reaction column. Fatty acid alkyl ester isevaporated in a suitable zone such as the sump evaporator and preferablyreturned at least partly to the column as vapor phase above the sump.The fatty acid triglyceride produced is separated from sodium carbonateand purified by conventional methods.

The invention is desribed in more detail with reference to theaccompanying drawings.

FIG. 1 diagrammatically illustrates an installation for carrying out theprocess according to the invention in non-continuous or batch fashion.

FIG. 2 diagrammatically illustrates the reactor portion of a process forcontinuously carrying out the present invention.

In the installation shown in FIG. 1, the fatty acid alkyl esters asdescribed above are fed through a pipe I to a heat exchanger 2 and,after heating, are fed through pipes 3 and 4 to a stirred reactor 5which is designed to be heated by a heating system 6. The fatty acidalkyl ester is heated to its boiling temperature and dried in thereactor unless this feedstock has already been dried. A mixture of driedsodium carbonate and glycerol is fed to the reactor through a pipe 7.The C₁ -C₄ alcohol formed during the reaction, which contains part ofthe fatty acid alkyl ester, is removed at the head of the reactorthrough a pipe 8 and fed to a rectification column 9. Fatty acid alkylester separated off at the bottom of the column is returned to thereactor 5 through a pipe 10. The rectified C₁ -C₄ alcohol is removed atthe head of column 9 and fed to condenser 12 through pipe 11. Part ofthe alcohol can be returned as reflux to the column 9 through pipe 13.The rest of the alcohol is fed through pipe 14 to a storage container 15for further use.

Through an alternative arrangement of pipes 7, 3 and 16, therectification column 9 can be charged with a mixture of sodium carbonateand glycerol, so that not only rectification, but also a reaction offatty acid alkyl esters takes place in the column. Glyceride formed inthis reaction is returned to the reactor 5 together with unreacted fattyacid alkyl ester.

The installation is connected by pipe 17 to vacuum pump 18 and isoperated under a light vacuum so that the reaction can be carried out ata lower temperature.

On completion of the reaction, pipe 14 is switched from the storagecontainer 15 to a storage container 19.

At elevated temperature and under a relatively high vacuum, theunreacted ester is distilled off from the reactor 5, condensed in thecondenser 12 and intermediately stored in the storage container 19.

The fatty acid alkyl ester distilled off is returned to the reactor 5through a pipe 20 for the next batch.

After distillation of the fatty acid alkyl ester, a mixture consistingessentially of triglyceride and sodium carbonate is removed from thebottom of the reactor 5 and is fed through pipe 21 to separator 22 wherethe mixture is separated into its constituents. The triglyceride isremoved through pipe 23 and the solid separated off through pipe 24.

The principal features of the process carried out as shown in FIG. 1 areas follows:

1. A mixture of dry sodium carbonate in dry glycerol is used as thecatalyst. Sodium carbonate is sufficiently soluble in the glycerol, butnot in the triglyceride, so that it is filtered off for reuse from thereaction product on completion of the reaction phase. Where sodiummethylate or sodium hydroxide is used in accordance with the prior art,washing is necessary for this purpose. This leads to the formation of anemulsion and the catalyst cannot be reused.

2. The reaction, itself, is preferably controlled by addition of theglycerol phase, in which the sodium carbonate catalyst is dissolved, tothe fatty acid ester which is preferably already heated to the reactiontemperature. The addition rate is controlled, depending on the reactionvelocity, such that the solubility limit of the glycerol in the ester isnot significantly exceeded. Thus, the reaction takes place substantiallyin a homogeneous liquid phase, and the process is not adversely affectedby delays in boiling or by excessive foaming through evaporatingmethanol.

3. The major portion of the initial reaction is largely completedachieving an OH value of 10 or above and usually in the range of 10-40by the time that the addition of glycerol and sodium carbonate has beencompleted. The residual reaction which generally requires a longer timethan the initial reaction necessitates the addition of more fatty acidmethyl ester to increase or to maintain the excess of fatty acid esterand to achieve substantially full conversion as represented by OH valuesless than 10 and preferably less than 5. The addition of this estercomponent at the beginning of the reaction would not accomplish thisreduction or conversion of hydroxyl groups. Instead, the reaction wouldstagnate in an OH value range of from about 10 to 40. The reactionmixture would continue boiling even in the after-reaction phase, i.e.for constant pressure, the reaction temperature would have to becontrolled in such a way that part of the methyl ester always evaporatesand is returned as reflux to the reactor, traces of reaction methanolbeing removed from the reaction mixture.

4. On completion of the residual reaction containing essentially onlytriglycerides and excess fatty acid alkyl ester, excess ester isdistilled off under as low a pressure as possible to keep thetemperature in the reactor low. Apart from the catalyst, only the crudetriglyceride is then present in the reactor. The methyl ester distilledoff may be returned with the next batch.

5. The sodium carbonate which precipitates with formation of thetriglyceride is separated off by filtration, centrifugation or otheradequate separation techniques. Filtration is preferably carried out at40° to 800° C. The catalyst filtered off is preferably reused.

6. The crude glyceride is then worked up solely through distillationstages which have not been shown. There is generally no need forbleaching and/or washing.

A continuous embodiment of the process according to the invention isdescribed with reference to FIG. 2.

Glycerol and sodium carbonate are introduced into mixing vessel 25through pipes 26 and 27, respectively, in such a way that the sodiumcarbonate dissolves in the glycerol. The solution is heated to thereaction temperature in heat exchanger 28 and fed in the liquid phaseonto the uppermost plate of reaction column 29. This solution andrecycled fatty acid alkyl ester comprises a liquid phase which flowsdownwardly in column 29.

Fatty acid alkyl ester is fed through pipe 30 to heat exchanger 31 inwhich it is evaporated, superheated in relation to the reactionconditions (temperature and pressure) and fed in this form assuperheated vapor to the middle part of the reaction column 29 throughpipe 32 for the initial reaction and through pipe 33 for the residualreaction. As the liquid phase flows downwardly through the column, partof the alkyl ester is condensed and reacted forming glyceride andmethanol as reaction products. The methanol evaporates and flows to thehead of column 29 as a mixture with superheated ester feedstock. As thevapor flows to the head of the column, the methyl ester contentdecreases while the methanol content continues to increase.

In the rectification column 34 of the reaction column 29, the remainingalkyl ester is separated off from the vapor phase. It passes as liquidphase back to the uppermost plate of the reaction column while thereaction alcohol is condensed in condenser 35. A partial stream of thealcohol is returned to the rectification column 34 while the major partis removed from the system through pipe 36 in accordance with the massbalance of the entire reaction alcohol.

Additional fatty acid alkyl ester required for the residual reaction isfed into the reaction column through pipe 33 below the first point ofintroduction for the fatty acid alkyl ester. Preferably, the alkyl esterintroduced in pipe 32 is separated by 2 to 5 plates in column 29.

The triglyceride formed collects in the sump of the reaction column 29with the corresponding excess of fatty acid alkyl ester. It iscirculated through a sump evaporator 37, methyl ester being evaporatedin such a quantity that the hydraulic function of the lowermost reactionplate of the reaction column 29 is guaranteed. The product stream of theglyceride is separated off from the circulating stream through pipe 38.The residual alkyl ester has to be distilled off from this productstream in a following distillation stage (not shown). It may be returnedto the reaction through the pipe 30 or employed for other purposes.

The pressure and temperature in the reaction column 29 are adjusted withrespect to the alkyl ester to be reacted in such a way that the alkylester may be fed in as superheated vapor.

One particular feature of carrying out the reaction in this way is thata boiling equilibrium between vapor phase and liquid phase prevails inthe lower part of the reaction column while the transfer of materialbetween liquid phase and vapor phase is determined by absorption anddesorption in the upper part of the column.

The process according to the invention is further illustrated in thefollowing examples.

EXAMPLE 1

2,000 g first-cut (C₆ -C₁₂) methyl ester are introduced into a 4-literglass flask.

The ester was dried for 25 minutes at 150° C./300 mbar. 280 g glycerolcontaining 13 g dissolved sodium carbonate were continuously introducedover a period 2.5 h. The reaction product, methanol, evaporated duringintroduction of the glycerol at a sump temperature of 140°-155° C. andunder a system pressure of 350-300 mbar. The vapor passed through anunregulated packed column with uncontrolled backflow. The vapor issuingat the head of the column was condensed.

After a reaction time of 3 h, another 200 g first-cut methyl ester wereintroduced into the reactor over a period of 1/2 h.

Over a reaction time of 2.5 h to 4.5 h at 300 mbar, the sump temperaturerose with refluxing from 155° to 180° C. The sump temperature of 180° C.and the system pressure of 300 mbar were maintained until the reactionwas over after a reaction time of 8 h.

A total of 276 g distillate was collected. After 8.5 h, a sump sampleshowed an OH value of 4.6 and an acid value of less than 0.1. The colorvalues of the sump were 6.0 yellow and 1.3 red.

The sump was then filtered through PRIMISIL® (filtration aid) toseparate off the precipitated catalyst.

500 g first-cut methyl ester were distilled off first from the retort ata temperature of 145° to 205° C. and under a pressure of 150 to 60 mbar.48.3 g dark-yellow colored head fraction were then distilled off at 170°to 247° C. under a pressure of 24 to 1 mbar.

The triglycerides were distilled over at 250° C. under a pressure of 1mbar. A product containing 91.2% triglycerides having a color value of 3yellow and 0.5 red distilled over whereof 85.5% had a color value of 2yellow and 0.5 red.

Towards the end of distillation, the distillate darkened again with 16.5g dark-brown residue remaining in the sump.

EXAMPLE 2

70 kg first-cut methyl ester were introduced into a nitrogenpurged100-liter reactor and heated to 150° C. under a vacuum of 300 mbar.

460 g soda powder were then dissolved in 9.3 kg glycerol. Theglycerol/catalyst mixture was introduced into the boiling organic phaseover a period of 4 h.

From the beginning of the glycerol addition, the components reacted withone another and a methanol/ester mixture evaporated. The vapor wasrectified. The reaction product, methanol, was removed from the systemas head condensate. After addition of the glycerol, another 7 kgfirst-cut methyl ester were introduced into the boiling reaction mixtureover a period of 1.5 h.

To keep the sump mixture boiling under reflux, the sump temperature wasincreased to 180° C. The pressure remained at 300 mbar. After a reactiontime of 11.25 h, the sump sample showed an OH value of 5.1.

The entire methanol condensate was then removed from the condensatereceiver.

To remove the unreacted ester, the ester was distilled off, bypassingthe column, at sump temperatures of up to 183° C. and under a vacuumfalling to 1.5 mbar, condensed and separately collected. Afterdistillation of the residual ester, the sump sample showed an OH valueof 3.0.

We claim:
 1. A process for the production of triglycerides of fattyacids which comprises:a) initially reacting a mixture of alkali metalcarbonate catalyst and glycerol with a substantial molar excess of a C₁-C₄ alkyl ester of C₆ -C₂₂ fatty acid at a temperature between about150° C. and 250° C. at less than atmospheric pressure and undersubstantially anhydrous conditions to produce an initial reactionmixture containing the corresponding triglycerides of said fatty acids,and partially reacted glycerol with unreacted hydroxyl groups, b)thereafter, reacting at least a portion of said initial reaction mixturewith additional C₁ -C₄ alkyl ester of C₆ -C₂₂ fatty acid underconditions to achieve substantially full conversion of said unreactedhydroxyl groups, and c) separating a product containing thecorresponding triglycerides of said fatty acids from unreacted alkylester and from said alkali metal carbonate catalyst.
 2. The process ofclaim 1 in which the molar ratio of glycerol to said alkyl ester isbetween about 0.15:1 and about 0.30:1.
 3. The process of claim 1 inwhich said alkali metal carbonate comprises sodium carbonate.
 4. Theprocess of claim 1 in which said alkyl ester is a methyl ester.
 5. Theprocess of claim 1 in which said alkyl ester comprises a C₁ -C₄ alkylester of C₆ -C₁₂ fatty acids.
 6. The process of claim 1 in which saidalkyl ester comprises a methyl ester of C₆ -C₁₂ fatty acids.
 7. Theprocess of claim 1 in which said initial reaction from step "a" isadmixed with at least 10% additional alkyl ester based on the said alkylester employed in step "a".
 8. The process of claim 11 in whichconditions are maintained such that the C₁ -C₄ alcohols formed in saidreaction are continuously distilled from said reaction mixture togetherwith excess alkyl ester.
 9. The process of claim 8 in which distilledmaterial is rectified and at least a portion of the alkyl ester isrecycled to step a or step b.
 10. The process of claim 1 in which saidinitial reaction of step a is carried out to achieve hydroxyl conversionrepresented by an OH value between about 10-40.
 11. The process of claim1 in which said reaction of step b is carried out to achieve hydroxylconversion represented by an OH value less than about
 10. 12. Theprocess of claim 1 in which said initial reaction of step a is carriedout to achieve hydroxyl conversion represented by an OH value less thanabout
 5. 13. The process of claim 1 in which said substantiallyanhydrous conditions include a water content less than about 1% in saidreaction mixture.
 14. The process of claim in which said substantiallyanhydrous conditions include a water content less than about 0.1% insaid reaction mixture.
 15. The process of claim in which said alkalimetal carbonate catalyst and glycerol are dried prior to admixing withsaid alkyl ester.
 16. The process of claim 1 in which said alkali metalcarbonate catalyst is dissolved in said glycerol prior to admixture withsaid alkyl ester.
 17. The process of claim 1 in which said glycerol isadmixed with said alkyl ester at a rate controlled such that theglycerol remains substantially soluble in said initial reaction mixtureand the said step "b" reaction with additional alkyl ester is initiatedafter addition of all of said glycerol in step a.
 18. The process ofclaim 1 in which unreacted alkyl ester is first separated from saidtriglyceride and said alkali metal carbonate catalyst is separated fromthe remaining triglyceride by filtration or centrifugation.
 19. Aprocess for the production of triglycerides of fatty acids whichcomprises:a) adding a mixture of dry sodium carbonate and glycerol to adried C₁ -C₄ alkyl ester of C₆ -C₂₂ fatty acid which is heated to atemperature of between about 150° C. to about 250° C. in a quantitycorresponding to a molar ratio of glycerol to fatty acid alkyl ester ofbetween about 0.15:1 to about 0.30:1 and at a rate such that theglycerol remains substantially soluble in the resulting reactionmixture, b) after addition of the glycerol, adding more of said alkylester to the reaction mixture which is maintained under boilingconditions in a quantity of at least 10%, based on the fatty acid alkylester used in step a), to react the unreacted hydroxyl groups of theglycerol, c) maintaining the reaction under a light vacuum andcontinuously distilling off C₁ -C₄ alcohol which is formed, d) producinga reaction mixture which consists predominantly of fatty acidtriglyceride, excess fatty acid alkyl ester and sodium carbonate, anddistilling off said excess alkyl ester, e) separating said sodiumcarbonate from said triglyceride, and f) further purifying saidtriglyceride.
 20. The process of claim 1 in which said fatty acid alkylester is methyl.
 21. The process of claim 19 in which:said mixture ofsodium carbonate and glycerol is fed into the upper part of amulti-plate reaction column at an elevated temperature; said fatty acidalkyl ester is fed into a mid portion of said reaction column at a pointbelow said mixture in the form of superheated vapor and reacts with saidglycerol resulting in a downflowing mixture of triglyceride, catalystand unreacted glycerol; additional fatty acid alkyl ester in the form ofsuperheated vapor is fed into said reaction column at a point below saidmid portion to react unreacted glycerol in said downflowing mixture; C₁-C₄ alcohol and fatty acid alkyl ester are rectified in a rectificationcolumn in communication with said reaction column and the C₁ -C₄ alcoholis removed overhead,and triglyceride/fatty acid alkyl ester/sodiumcarbonate mixture is removed from the sump of said reaction column;fatty acid alkyl ester is evaporated in a sump evaporator and returnedat least partly to the column as vapor phase above the sump and fattyacid triglyceride obtained is separated from sodium carbonate.